Map Emplace_hint() function in C++ STL
In this tutorial, we will discuss the emplace_hint() function in C++ with its syntax, example, benefits, and applications.
The emplace_hint() method in the C++ Standard Template Library (STL) enables you to quickly insert items into specific containers (like map and unordered_map) by using a hint that you give, which can be the location where the element is anticipated to be inserted in the container. Knowing where the new element should be put makes this function more effective than emplace() function.
Syntax:
It has the following syntax:
iterator emplace_hint(const_iterator hint, Args... args);
- hint: A hint is a constant iterator that indicates where to place the new element. Depending on how the container is implemented internally and whether it uses hashing or ordering, the insertion may or may not occur at the point indicated by the hint.
- Args... args: The arguments are needed in the constructor to create the new element. The constructor of the element type receives these inputs.
- The return value of emplace_hint() is an iterator pointing to the newly inserted element.
Example:
Let us see an example to understand the use of the emplace_hint() function in C++:
#include <iostream>
#include <map>
using namespace std;
int main() {
map<int, string> myMap;
// Insert elements using emplace_hint()
auto hint = myMap.end(); // Set the hint to the end initially (optional)
hint = myMap.emplace_hint(hint, 2, "Two");
hint = myMap.emplace_hint(hint, 1, "One");
hint = myMap.emplace_hint(hint, 3, "Three");
// Print the map
for (const auto& pair : myMap) {
cout << pair.first << ": " << pair.second << endl;
}
return 0;
}
Output:
![Map Emplace_hint() function in C++ STL](https://static.tutorialandexample.com/cpp/map-emplace-hint-function-in-cpp-stll1.png)
Inserting elements in a loop with emplace_hint().
#include <iostream>
#include <map>
using namespace std;
int main() {
map<int, string> myMap;
// Insert elements using emplace_hint() in a loop
for (int i = 0; i < 10; ++i) {
auto hint = myMap.end(); // Set the hint to the end initially (optional)
hint = myMap.emplace_hint(hint, i, "Element " + std::to_string(i));
}
// Print the map
for (const auto& pair : myMap) {
cout << pair.first << ": " << pair.second << endl;
}
return 0;
}
Output:
![Map Emplace_hint() function in C++ STL](https://static.tutorialandexample.com/cpp/map-emplace-hint-function-in-cpp-stll2.png)
Benefits of Map Emplace_hint() function in C++ STL:
The C++ STL's emplace_hint() function has various advantages. Some main advantages of the emplace_hint() function are as follows:
Better Complexity Assurances: When using the emplace_hint() function with the right hint, you can insert elements with better complexity assurances. For instance, if the clue is close to the actual insertion point in a balanced binary search tree-based container like a map, the insertion operation may have logarithmic complexity O(log n) rather than linear complexity O(n).
Customized Insertion Position: The position in which the new element should be put can be customized using the emplace_hint() function. A hint iterator pointing to the spot can be provided where the new element is supposed to store. The container will utilize this tip to choose the best insertion position based on its internal sorting or hashing algorithm.
Performance Gains: The main benefit of using the emplace_hint() function is that it inserts elements into ordered associative containers (like std::map) or unordered associative containers (like std::unordered_map) more quickly. The container can prevent needless reordering (in the case of std::map) or rehashing (in the case of std::unordered_map) by giving a hint about the insertion position. Faster insertion times may result, mainly when working with big containers.
Reduced Iterator Invalidations: When inserting elements into ordered associative containers, giving a right hint can reduce the number of iterator invalidations. For instance, using the emplace_hint() function with a correctly updated hint when putting elements into a loop ensure that the hint is still valid after each iteration without repeatedly recalculating the hint.
NOTE:
The advantages of the emplace_hint() function largely depend on the properties of the container, the data being inserted, and the precision of the hints offered, and it is crucial to remember. If the suggestions are not picked carefully, the performance advantage brought about by using the emplace_hint() function may occasionally be insignificant or even result in worse performance.
Overall, the emplace_hint() function is a robust tool for insertion performance optimization in some cases. Still, thorough evaluation and profiling are needed to ensure that it actually delivers the intended results for a given use case. When it is used without indications, emplace() or insert() will frequently still perform well for most applications.
Applications of Map Emplace_hint() function in C++ STL:
When you know the insertion location or want to enhance the performance of inserting elements into ordered or unordered associative containers, the C++ STL's emplace_hint() method can be helpful in various situations. The following are some typical uses for emplace_hint():
Fine-grained Control: The emplace_hint() function enables you to effectively implement this fine-grained control when inserting elements in the container at precise locations, such as immediately before or after other elements.
Priority Queues: You can use the emplace_hint() function to insert elements with hints representing their priority when creating a priority queue using a map or any other ordered associative container.
Iterative element insertion: The emplace_hint() function can be helpful to maintain track of an updated hint in situations where you are adding elements into a container inside a loop. Using this method, you can avoid recalculating the hint after each iteration, enhancing the loop's overall performance.
Batch Insertion: Using the emplace_hint() function with the right hint can increase efficiency when inserting several pieces into a container simultaneously. You can reduce the container's need to reorganize or rehash after each insertion by giving a tip close to the anticipated insertion spot.
Reduce Iterator Invalidations: If you have ordered associative containers with long-lived iterators to the elements, using the emplace_hint() function can assist in reducing iterator invalidations while adding new elements.
Real-time Applications: Applications for immediate information. Utilizing the emplace_hint() function with the appropriate suggestions helps reduce the amount of time needed for element insertion in real-time applications where efficiency is crucial. It is crucial when quick data updates like video games, simulations, or financial systems are typical.